Here's my edits and stuff:
"The central companionway stretch down, down, down-"
I believe you may want to use 'stretched' instead of 'stretch' here
"squeezing through the almost foot-thick layer of lead shielding that turned a space originally meant to hot-bunk 25 crewmen into a space that could barely fit 12."
I would re-phrase this somehow, I had to read it a few times before I understood what you were talking about.
"Tucking her feet into the handles mounted on the inside of the hatch, she braced her arms against the side of the passage and yanked the thick plug of lead shut."
Not an edit, I just wanted to say thank you for accurately describing how moving in zero-g works. So many people get so much wrong and your writing seems spot on.
"Jones gave a wide yawn,"
instead of gave, use 'let out'
"That pretty camouflage of yours is working I hope, girlie?"
this dialogue seems a bit stilted. re-phrase to something like "That pretty camouflage of yours is working, right girlie?"
""Well I'll be damned. They shoulda never let women into this sad excuse for a space navy, I tell you. Sleep well, girlie.""
Just a quick note, because the crew area is round the clock hotbunked (at least, that's what you said), there would probably be other people in there with the two of them. Maybe add a line somewhere of "Jenkins from engineering" saying something like "Shaddap, I'm troina sleep 'ere" or something. Not required, but I think it would improve the liveliness of the ship.
"not that the term mattered in zero-gravity- of the sleeping pod."
You don't need the second "-" after gravity.
"it was important as hell if they were gonna wake her during her shift."
This isn't her shift, she's of duty right now. So just add off duty in front of shift and you're good to go."
"she held the slide rule, notebook and a couple pencils in her teeth."
Just a comment: That's a big fucken mouth, holy shit.
"Miss Perryman- will your radar jammers work in an atmosphere"
remove the "an" it isn't needed given that the only atmosphere they would be interacting with is Earth's
"Plan is to wait for the last possible moment so re-entry flux hides out signature from their ground radar."
Out should be our
"Stow panels, trim and lock rads for atmo, please."
Just a comment: This whole little section is awesome.
"There was an uncomfortable silence.
'Miss Perryman?'"
Just a comment: Comedy gold, I actually laughed out loud.
"'Mister Groenberg, casualties?'"
Just a comment: Your writing through this section is impeccable. The action is tight, the physics right, it's beautiful, I can't find anything wrong.
"Cocooned in surgical tubing and gauze, the severed head of Colonel Vladimir Mikhaylovich Komarov stared blankly out the window"
Just a comment: I think it's really neat how you paralleled the soviet dog experiments, where they kept severed dog heads alive for hours.
All around: amazing tale, I hope you write more in the future. I suggest tossing this into Grammarly to catch any little things I missed.